Science > Biology > Soil Management > Soil and its Types
Soil is one of the three major natural resources, alongside air and water required for sustenance of life. It is the upper layer of earth in which plants grow, a black or dark brown material typically consisting of a mixture of organic remains, clay, and rock particles. It is made of stones, pebbles, sand, fine particles as well as organic substances. All the living things in it, plus essential materials that these organisms use to survive, form the soil ecosystem.
The study of this ecosystem is important to understand the interaction and relation between organisms in the soil and the environment that surrounds them. Soils vary greatly in their chemical and physical properties which depend on their age and on the conditions (parent material, climate, topography, and vegetation) under which they were formed.
Importance of Soils:
- They provide support to plants by holding the roots firmly and help in providing water and nourishment, minerals to the plants.
- They soil Help in the growth of the plant and are important for agriculture. Agriculture helps in satisfying the need for food clothing and shelter to all.
- Soils provide adequate aeration in the soil. They provide air for gaseous exchange between the roots and the atmosphere. They protect plants from erosion, and other destructive physical, chemical, and biological activity.
- The survival of plants is very essential, because they are prime producers, as they can prepare their own food in the process called photosynthesis. Animals are dependent on plants for survival. Thus animals are indirectly dependent on the soil for survival and nourishment.
- They are home to many organisms such as worms and termites. Insects and microbes live in the soils and depend on soils for food and air. Soil provides the needed moisture and air for the breakdown of organic matter. It provides a home for many organisms to lay and hatch eggs and rodents to give birth to new offspring.
- As the rainwater continues its way downwards through the layers in the ground, it is filtered from dust, chemicals, and other contaminants. Thus water gets purified. Hence the underground water is one of the purest sources of water.
- Soils are used for the construction of foundations, roadbeds, dams, and buildings.
Soil Ecosystem:
Soils are rich ecosystems, composed of both living (biotic) and non-living (abiotic) matter with a wide variety of interaction between them. Soils play a very important role in all natural ecological cycles: carbon, nitrogen, oxygen, water, and nutrient. The soil provides a number of other critical ecosystem services. These services include waste decomposition, water filtration system, degrading environmental contaminants, protection for seeds, a support system for plants, retention, and delivery of nutrients, etc. The diversity and abundance of life that exists within the soil is greater than in any other ecosystem. A handful of soil can contain billions of different organisms that play a critical role in soil quality to support plant growth. All the members of this ecosystem, together with their abiotic factors are active to ensure the survival of the ecosystem.
Formation of Soil:
All soils initially come from rocks, this is termed the ‘parent material’. The Parent Material may be directly below the soil, or at great distances away if wind, water or glaciers have transported the soil. The process by which rocks are transformed into the soil is called weathering. During this process, rocks are converted into smaller and smaller particles and ultimately they are turned into soil. Layers of this soil spread over the surface of the earth. The weathering of rocks takes places due to the effects of rain, rainwater, river, wind and continuous change of weather. It takes about 800 to 1000 years to form a 2.5 mm thick layer of fertile soil. Weathering can be a physical, chemical or biological process:
- Physical Weathering: The breakdown of rocks from the result of a mechanical action due to wind, rain, flowing water, temperature changes, abrasion (when rocks collide with each other) or frost. Extreme heat, extreme cold and a large change in day and night temperatures cause the weathering of rocks.
- Chemical Weathering: The breakdown of rocks through a change in their chemical composition. This can happen when the minerals within rocks react with water, air or other chemicals.
- Biological Weathering: Biological activities by rodents like rats and bandicoots cause weathering due to burrowing activity. The growth of roots in the soil in crevices of rocks causes the weathering of rocks. Plants, insects, and animals live on soil, grow on soil and ultimately die and decay into the soil. It also adds to the weathering of soil.
Relief refers to the landscape position and the slopes it has. On steep, long slopes water runs down faster and erode the surfaces of slopes. The effect of this erosion is that there will be poor soils on the slopes and richer deposits at the foot of the slopes. At the same time, the soil on slopes may be exposed to more direct sunlight, which may dry out soil moisture and render it less fertile. The soils left on steep hills are usually shallower. Transported soils include alluvial (water transported), colluvial (gravity transported), and aeolian (wind transported) soils.
Types of Soils:
Weathering of rocks produces small particles of various materials, which include sand and clay. The relative amount of sand and clay depends upon the rock from which the particles were formed.
Types of Soils on the Basis of Texture:
The size of particles, decide the texture of soils. On the basis of texture, soils are classified into four types. viz. sandy soils, clayey soils, loamy and silt
- Sandy Soils: If the soil contains a greater proportion of big particles it is called sandy soil. The particles are quite large and hence they cannot fit closely together. Thus there are large spaces between the particles which are filled by air. Hence sandy soil is highly aerated. Water can drain down through these spaces. Hence It has the least capacity of holding water. In general, particles of sandy soil are well aerated, light and dry.
- Clayey Soils: If the proportion of fine particles is relatively higher, then it is called clayey soil. It has the highest capacity of holding water. The particles are very fine and hence they can fit closely together. Thus there are small spaces between the particles which are filled with water particles leaving almost no space for air. Hence clayey soil is ill aerated. Water cannot drain down through these small spaces. Hence It has the highest capacity of holding water. In general, particles of clayey soil are ill aerated, heavy and moist.
- Loamy Soils: If the amount of large and fine particles is about the same, then the soil is called loamy. Loamy soil is a mixture of sand and clay. Its water holding capacity is medium (right for proper growth of plants). Loamy soil also has humus in it and it is well aerated. The best topsoil for growing plants is loam.
- Silt: In this type fine and medium-sized particle medium-sized particles are seen. Silt occurs as a deposit in river beds. The size of the silt particles is between those of sand and clay. Its water holding capacity is medium and is well aerated.
Types of Soil on the Basis of Uses:
Depending upon the uses of soils, they are classified into three types viz. China clay, clay, and loamy soils.
- China Clay: It is also called Kaolin because it is found near the Kaolin mountain in China. It is white in colour. It is used for making crockery, tiles for bathrooms, tanks, and laboratory apparatus, etc.
- Clay: It is a special type of China clay. It is white in colour and is used for making idols and statues.
- Loamy Soil: It is a special type of China clay. It is white in colour and is used for making idols and statues.
Note: Different types of oxides are used to decorate and paint earthenwares and porcelain articles. Copper oxide is used to obtain green colour and iron oxide is used to obtain a red colour.